1. Technical Field
The present invention relates to a rotor of a motor which uses magnets and a method of production of such a rotor.
2. Description of the Related Art
As described in Japanese Patent No. 4708445 etc., the rotor of a motor includes a plurality of magnets in the circumferential direction and axial direction. When using magnets as parts of a motor, the higher the magnetic flux densities of the magnets, the greater the gap magnetic flux of the motor and the greater the torque which the motor generates. In this regard, the higher the magnetic flux densities of the magnets, the higher the back electromotive force becomes. For this reason, normally a d-axis current is run in the magnetic flux direction in accordance with the back electromotive force. Due to this, it is necessary to lower the voltage applied to the motor to the input voltage or less. Such a d-axis current is generally controlled by an open loop. When the back electromotive force fluctuates, it is necessary to run extra d-axis current as reactive current, so the motor efficiency falls.
In this regard, magnets are produced by a plurality of manufacturers. Therefore, the magnetic flux densities of magnets differ slightly depending on the manufacturer. For example, the magnetic flux density of a magnet which is produced by a Company A will be 1.27 to 1.33 T, the magnetic flux density of a magnet which is produced by a Company B will be 1.30 to 1.36 T, and the magnetic flux density of a magnet which is produced by a Company C will be 1.33 to 1.39 T.
When using magnets with different magnetic flux densities at the same motor, there is the problem of a variation in torque of the motor depending on the type of magnets which are used. Furthermore, it is necessary to run a reactive current, so there is also the problem that the motor efficiency falls.
The present invention was made in consideration of this situation and has as its object the provision of a rotor of a motor which is free of variation in torque even if using magnets of different magnetic flux densities at the same motor and a method of production of such a rotor.